An LTE network consists of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) evolved NodeB (eNB) and an Evolved Packet Core (EPC), and the network is flattened; wherein the E-UTRAN comprises a set of eNBs connected with the EPC through an S1 interface and the eNBs connect with each other through an X2 interface. The S1 and X2 interfaces are logical interfaces. One EPC can manage one or more eNBs, one eNB can be controlled by multiple EPCs, and one eNB can manage one or more cells.
The Self-Organizing Network (SON) technology is a technology capable of automatically configuring and optimizing the network, which is characterized in self-configuration and self-optimization. The technology is applied in the LTE system to enable the LTE eNB to automatically configure a network parameter according to certain measurement and perform an automatic optimization according to the change of the network, thereby maintaining the optimal network performance and saving a great amount of manpower and material resources.
As for the self-optimization of the handover parameter of the LTE system, the parameter related to a cell re-selection and handover is required to be optimized according to a certain algorithm, operation condition of the network and handover-related measurement, so as to improve the network performance. Wherein the handover herein refers to handover within the LTE system or handover between the systems, wherein
(1) a handover between the systems is a handover to the Universal Terrestrial Radio Access Network (UTRAN), Global System for Mobile Communication (GSM) or Code Division Multiple Access (CDMA) system;
(2) a handover process of a terminal in the network, i.e. a handover within the system, is that: the network side makes a handover decision on the basis of a certain handover algorithm according to the signal quality of the current cell and a neighboring cell reported by the terminal and then notifies the terminal to execute a specific handover flow according to the handover decision.
During the handover, inappropriate setting of the handover parameter will result in a ping-pong handover, handover failure and Radio Link Failure (RLF), which are undesired and bring negative effect to user experience and result in waste of the network resources. Therefore, for a self-optimization of the handover parameter, an adjustment of the handover parameter is based on accurately determining of the handover failure and undesired handover scenario.
RLF will occur to a User Equipment (UE) in the case of very poor radio link signal and the UE will perform reestablishment of Radio Resource Control (RRC). When the UE performs the RRC reestablishment, a target cell is obtained via a cell selection procedure. A source eNB or target eNB will keep the user information for reestablishing the RRC in the case of the handover failure during the handover process.
The UE will carry a UE-Identity which includes a Cell Radio Network Temporary Identifier (C-RNTI) of the UE, a short Medium Access Control Integrity protection (shortMAC-I) which is a short Medium Access Control Integrity check value and a Physical Cell Identity (PCI) in an RRC reestablishment request message, wherein                the C-RNTI is allocated in the source cell (for the scenario of the handover failure), or allocated in a cell triggering the RRC reestablishment (for other scenarios);        the PCI is the physical identity of the source cell (for the scenario of the handover failure), or the physical identity of a cell triggering the RRC reestablishment (for other scenarios);        the shortMAC-I is calculated by using a KRRCint key of the source cell (for the scenario of the handover failure) or a cell triggering the RRC reestablishment and an integrity protection algorithm; the PCI, C-RNTI and Evolved Cell Global Identifier (ECGI) are input, wherein the PCI and C-RNTI are contained in the RRC reestablishment message and the ECGI is an ECGI of a target cell selected by the UE during the RRC reestablishment.        
In an existing handover, three typical undesired handover scenarios are as follows:
first: a scenario of a too-late handover, as shown in FIG. 1, RLF occurs to a terminal (i.e. UE) in a cell b under an eNB B, then the UE attempts to perform an RRC reestablishment in a cell a under an eNB A, which indicates that the handover of the UE from the cell b to cell a is too late;
second: a scenario of a too-early handover, as shown in FIG. 2, soon after a handover of a UE from a cell a under an eNB A to a cell b under an eNB B is performed, an RLF occurs in the cell b and the UE subsequently selects the cell a under the eNB A to perform an RRC reestablishment, that is the UE returns to the cell a before the handover to perform the RRC reestablishment, which indicates that the previous handover of the UE from the cell a to cell b is too early;
third: a scenario of selecting a wrong cell during a handover, as shown in FIG. 3, wherein an RLF occurs soon after a handover of a UE from a cell c under an eNB C to a cell b under an eNB B is performed, and the UE subsequently performs an RRC reestablishment in a cell a under an eNB A, which indicates that the cell b under the eNB B which is selected before the handover is a wrong target cell and the correct target cell should be the cell a under the eNB A, that is, the UE should directly performs the handover from the cell c under the eNB C to the cell a under the eNB A.
For the aforementioned three typical undesired handover scenarios, how to determine the type of an undesired handover is a key problem, and an existing method for the determining comprises the following steps:
step 1: an eNB A notifies an eNB B of RLF information;
wherein the RLF information comprises: a PCI of a cell where the RLF occurs, a PCI or an ECGI of a cell attempting an RRC reestablishment, and a C-RNTI of a UE in the cell where the RLF occurs, wherein the PCI of the cell where the RLF occurs and the C-RNTI information of the UE in the cell where the RLF occurs are from the RRC reestablishment message of the UE received by the eNB A;
step 2: the eNB B receives the RLF information and performs the determining according to UE context information contained in the RLF information, namely information of the PCI and C-RNTI:                if the UE is just handed over from a cell a under the eNB A, then the eNB B determines that the handover of the UE from the cell a to cell b is too early, as shown in FIG. 2 and notifies the eNB A of the result of the determining;        if the UE is just handed over from a cell c under an eNB C, then the eNB B determines that the target cell selected by the UE during the handover from the cell c to cell b is an error, as shown in FIG. 3, and the correct target cell is the cell a and the eNB B notifies the eNB C of the result of the determining;        otherwise, the eNB B then determines that the handover of the UE from the cell b to the cell a is too late, as shown in FIG. 1.        
At present, one problem existing in the method for determining a handover scenario is that the eNB A determines a cell where the RLF occurs and the eNB to which the cell belongs according to the PCI information in the RRC reestablishment message from the UE. In the case of PCI confusion, that is, the PCIs of the two cells are identical, the eNB A may identify a wrong cell where the RLF occurs and select a wrong target eNB receiving the RLF information when sending the RLF information, that is, the cell b where the RLF occurs and eNB B cannot be uniquely identified only by the PCI information in the RRC reestablishment message, thereby certainly resulting in an inaccurate optimization of a handover parameter and reducing the self-optimization function of the handover parameter.
Therefore, in order to avoid the aforementioned problem that an error occurs during sending RLF, which is possibly caused by the PCI confusion, the terminal should be further identified. Since the terminal is unique, if the terminal can be identified uniquely, then the cell where the terminal is located, namely the unique cell where an RLF occurs, can be accurately determined, thereby increasing the accuracy of an optimization of the handover parameter and enhancing the self-optimization function. Thus, how to identify a terminal in a handover scenario has become a problem to be solved.